1. Field of the Invention
The present invention relates to a clutch assembly which engages upon positive torque being provided by an input member to transfer the torque to an output member. More specifically, the present invention relates to a two-way over-running clutch assembly of a roller/ramp variety and the mechanism by which the rollers are retained and biased in the assembly.
2. Description of the Prior Art
Roller/ramp clutch assemblies are used in a wide variety of applications. One possible application is an automatic locking hub of a four-wheel drive vehicle. During operation of four-wheel drive vehicles, it is often desirable to disconnect the alternate drive wheels (usually the front wheels) of the vehicle from the remainder of the drive train. When disconnected, the alternate drive wheels can rotate freely with respect to the drive train and, accordingly, they are free to rotate without regard to the rotational speed of the drive train. At other times, it is preferred that the alternate drive wheels of the vehicle automatically lock to the drive train whenever there is relative disproportional rotation between the alternate drive wheels and the input member from the drive train. The above clutch assemblies have also been provided where the clutch assembly transfers torque in only one direction and where the torque can be transferred in two directions.
Currently, vehicles with part time four-wheel drive systems generally use one of three mechanisms to engage the alternate drive wheels, which are usually the front wheels. One mechanism is the center disconnect system. In this system, a spline coupling is actuated by a vacuum diaphragm, electrical solenoid or other system to connect and disconnect the front half-shafts together. When disconnected, relative movement between the inboard and outboard sides of the spline coupling is possible and no power is transmitted between them. When engaged, however, the axle is effectively solid and torque inputted through the drive shaft into the differential will be split between the front wheels. While this system is inexpensive, its drawbacks include noise when disengaged and high parasitic losses because the half shafts and differential are continuously driven by the rotating alternate drive wheels when the coupling is not engaged.
A second mechanism is the wheel end disconnect system. These systems use a spline coupling, similar to that discussed above, at the wheel end to connect and disconnect the half shaft from the wheel. The expense of this system is greater than the center disconnect system because it requires a separate clutching mechanism at each wheel. However, parasitic losses are lower and better fuel economy results. If of a manually actuated variety, the mechanism cannot be shifted during operation of the vehicle. Instead, the operator must stop the vehicle and engage the hub lock from outside the vehicle. For some vehicle owners this is inconvenient, but for others it is a desirable inconvenience because of its reliability over automatic systems of the same general type.
Another type of clutch assembly does not utilize a splined engagement. Rather, concentric driving and driven members are provided with the driving member having axial surfaces which face radially toward the other member. Upon each surface, a roller is loosely held. These assemblies are referred to as roller/ramp clutch assemblies. The rollers are inertially responsive to acceleration of the driving member and when rotational acceleration of the driving member occurs, the inertia of the rollers causes them to move along the surfaces toward a side edge of the surfaces. At the side edge, the distance between these surfaces and the driven member is less than the diameter of the roller and the roller contacts the driven member becoming engaged or locked in the wedge formed between the axial surfaces of the driving member and the circumference of the driven member. In some varieties, the rollers can move along the axial surfaces to either side. In other varieties, engagement with the driven member is only possible by movement of the roller to one side of the surface.
In these latter systems, however, complex mechanisms are used to retain the rollers into the grooves. The mechanisms have also generally failed to ensure that the rollers will engage between the driving and the driven members at the same time. Failure to provide for substantially simultaneous engagement results in disproportionate stresses being applied to the rollers, the driving member and the driven member. Additionally, non-simultaneous engagement of the rollers has the effect of making the engagement and disengagement more noticeable during operation of the vehicle.
Prior designs have also used a common biasing member to bias all of the rollers of the assembly to the center of the respective surfaces. As a result, greater biasing forces are required and a failure of the biasing member results in all of the rollers of the assembly being negatively affected.
It is to this latter type of assembly that the present invention particularly relates.
In view of the foregoing limitations and shortcomings of the prior art devices, as well as other disadvantages not specifically mentioned above, it should be apparent that there still exists a need in the art for an improved roller/ramp clutch assembly.
A primary object of this invention is therefore to fulfill that need by providing an over-running clutch assembly which ensures substantially simultaneous engagement and disengagement of the roller elements between the driving and driven members.
Another object of the present invention is to provide an overrunning clutch assembly which allows for independent biasing of the individual roller elements.
A further object of this invention is to provide an over-running clutch assembly which allows for two-way torque transfer/operation of the assembly.